Most exercising devices serve two purposes, to strengthen muscles and to rehabilitate muscles which have been damaged.
In contact and running sports, the knee is probably the most damaged portion of the body. It is important to strengthen the muscles in the hip, thigh and calf to prevent injury to muscles in these areas, and to assure proper rehabilitation of damaged muscles. Proper strengthening of these muscles in the hip, thigh and calf areas will prevent undue stress on the knee connecting tissue which is easily damaged. This is also true of the arm and back muscles which control the movements of the shoulders and elbow.
Heretofore, exercising devices have not utilized the full potential of stressing muscles throughout movement of a limb to fully strengthen adductor and abductor muscles of the hip. Strengthening the hip muscles and thigh muscles is extremely important in knee rehabilitation because any weak portion of the lower muscular system might result in reinjury of the previously damaged knee or other muscle.
For most efficient strengthening of these areas, it is necessary to isolate these muscles and restrain the rest of the body movement. In addition, it is important to position the body in an attitude similar to that in which the muscles will be doing their work. For example, most of the work done by muscles in the leg of an athlete is done while the leg is slightly bent at the knee and hip. Therefore, it is important to position the body such that the legs extend outwardly from the hip in a slightly bent position and the legs slightly bent at the knee to strengthen the muscles in the position that they are used.
Devices such as those disclosed in U.S. Pat. Nos. 3,120,954; 3,465,592; 3,495,824; and 3,822,599 generally use sophisticated hydraulic structures and pumps which add to the cost and complexity of the device and thereby reduce their availability to the general public.
Heretofore, devices which use weights have a fixed weight and as the limb, i.e. arm or leg, changes position the moment of force is changing and the force required to move the weight changes; therefore, the limb is not properly stressed throughout the range of movement. Further, the maximum force that the limb can exert generally increases as the limb moves from a bent position to a straightened position.